kubectl: refactor rollout history to be more configurable

ChangeCauseAnnotation is hardcoded in PrintRolloutHistory and it needs
to be overriden since other resources that may need to be added in
`kubectl rollout history` may not use it. Instead of adding one more
method in the factory, refactor the existing HistoryViewer interface
to accomodate the change.

pkg/kubectl/history.go

@@ -17,6 +17,7 @@ limitations under the License.
 package kubectl
 
 import (
+	"bytes"
 	"fmt"
 	"io"
 
@@ -34,9 +35,9 @@ const (
 	ChangeCauseAnnotation = "kubernetes.io/change-cause"
 )
 
-// HistoryViewer provides an interface for resources that can be rolled back.
+// HistoryViewer provides an interface for resources have historical information.
 type HistoryViewer interface {
-	History(namespace, name string) (HistoryInfo, error)
+	ViewHistory(namespace, name string, revision int64) (string, error)
 }
 
 func HistoryViewerFor(kind unversioned.GroupKind, c clientset.Interface) (HistoryViewer, error) {
@@ -47,68 +48,68 @@ func HistoryViewerFor(kind unversioned.GroupKind, c clientset.Interface) (Histor
 	return nil, fmt.Errorf("no history viewer has been implemented for %q", kind)
 }
 
-// HistoryInfo stores the mapping from revision to podTemplate;
-// note that change-cause annotation should be copied to podTemplate
-type HistoryInfo struct {
-	RevisionToTemplate map[int64]*api.PodTemplateSpec
-}
-
 type DeploymentHistoryViewer struct {
 	c clientset.Interface
 }
 
-// History returns a revision-to-replicaset map as the revision history of a deployment
-func (h *DeploymentHistoryViewer) History(namespace, name string) (HistoryInfo, error) {
-	historyInfo := HistoryInfo{
-		RevisionToTemplate: make(map[int64]*api.PodTemplateSpec),
-	}
+// ViewHistory returns a revision-to-replicaset map as the revision history of a deployment
+func (h *DeploymentHistoryViewer) ViewHistory(namespace, name string, revision int64) (string, error) {
 	deployment, err := h.c.Extensions().Deployments(namespace).Get(name)
 	if err != nil {
-		return historyInfo, fmt.Errorf("failed to retrieve deployment %s: %v", name, err)
+		return "", fmt.Errorf("failed to retrieve deployment %s: %v", name, err)
 	}
 	_, allOldRSs, newRS, err := deploymentutil.GetAllReplicaSets(deployment, h.c)
 	if err != nil {
-		return historyInfo, fmt.Errorf("failed to retrieve replica sets from deployment %s: %v", name, err)
+		return "", fmt.Errorf("failed to retrieve replica sets from deployment %s: %v", name, err)
 	}
 	allRSs := allOldRSs
 	if newRS != nil {
 		allRSs = append(allRSs, newRS)
 	}
+
+	historyInfo := make(map[int64]*api.PodTemplateSpec)
 	for _, rs := range allRSs {
 		v, err := deploymentutil.Revision(rs)
 		if err != nil {
 			continue
 		}
-		historyInfo.RevisionToTemplate[v] = &rs.Spec.Template
+		historyInfo[v] = &rs.Spec.Template
 		changeCause := getChangeCause(rs)
-		if historyInfo.RevisionToTemplate[v].Annotations == nil {
-			historyInfo.RevisionToTemplate[v].Annotations = make(map[string]string)
+		if historyInfo[v].Annotations == nil {
+			historyInfo[v].Annotations = make(map[string]string)
 		}
 		if len(changeCause) > 0 {
-			historyInfo.RevisionToTemplate[v].Annotations[ChangeCauseAnnotation] = changeCause
+			historyInfo[v].Annotations[ChangeCauseAnnotation] = changeCause
 		}
 	}
-	return historyInfo, nil
-}
 
-// PrintRolloutHistory prints a formatted table of the input revision history of the deployment
-func PrintRolloutHistory(historyInfo HistoryInfo, resource, name string) (string, error) {
-	if len(historyInfo.RevisionToTemplate) == 0 {
-		return fmt.Sprintf("No rollout history found in %s %q", resource, name), nil
+	if len(historyInfo) == 0 {
+		return "No rollout history found.", nil
 	}
+
+	if revision > 0 {
+		// Print details of a specific revision
+		template, ok := historyInfo[revision]
+		if !ok {
+			return "", fmt.Errorf("unable to find the specified revision")
+		}
+		buf := bytes.NewBuffer([]byte{})
+		DescribePodTemplate(template, buf)
+		return buf.String(), nil
+	}
+
 	// Sort the revisionToChangeCause map by revision
-	revisions := make([]int64, 0, len(historyInfo.RevisionToTemplate))
-	for r := range historyInfo.RevisionToTemplate {
+	revisions := make([]int64, 0, len(historyInfo))
+	for r := range historyInfo {
 		revisions = append(revisions, r)
 	}
 	sliceutil.SortInts64(revisions)
 
 	return tabbedString(func(out io.Writer) error {
-		fmt.Fprintf(out, "%s %q:\n", resource, name)
 		fmt.Fprintf(out, "REVISION\tCHANGE-CAUSE\n")
 		for _, r := range revisions {
 			// Find the change-cause of revision r
-			changeCause := historyInfo.RevisionToTemplate[r].Annotations[ChangeCauseAnnotation]
+			changeCause := historyInfo[r].Annotations[ChangeCauseAnnotation]
 			if len(changeCause) == 0 {
 				changeCause = "<none>"
 			}